For some obscure reason an advert for these things is following me from webpage to webpage . The description is below . What are they ? And how have I managed 65 years without them M6 x 9 & M6 x 12 SOLID BRASS SPREADING SLEEVE INSERT PRESS FIT WITH NYLON PELLET
Never had a need for those either Harry Looks like a plug for chipboard units maybe? So you can screw something to the side of a unit such as a light fitting - only going by the shallow depth.
Drill a hole. Push them in. Hold with spanner. Screw in a bolt or stud. The nylon ball deforms, opens the "legs" and the insert grips the hole. They're quite often used in electrical installations that use softer materials.
Thanks @Sandy Ground ! They are similar to the threaded Nutserts that you fit onto sheet metal . I must find a use for them soon !